Surgical Pathology Criteria

Type B2 Thymoma


Alternate / Historical Names

Diagnostic Criteria

Supplemental Studies


Differential Diagnosis

Type B1 Thymoma Type B2 Thymoma
Predominantly lymphocytes with inconspicuous epithelial cells Both lymphocytes and epithelial cell prominent
Numerous scattered pale medullary foci Only occasional medullary foci

Type B2 Thymoma Type B3 Thymoma
Both lymphocytes and epithelial cells are easy to see Predominantly epithelial with few lymphocytes
Lacks any epidermoid features Frequently has epidermoid differentiation (but lacks overt keratinization and bridges)
Epithelial CD5 negative Epithelial cells may be focally positive for CD5
Epithelial cell nuclei are large round vesicular with prominent nucleoli

Epithelial cell nuclei moderate in size, not typically large and vesicular

Type AB Thymoma Type B2 Thymoma
Epithelial cells have small oval to spindled nuclei with dispersed chromatin and inconspicuous nucleoli Epithelial cells have vesicular nuclei with prominent nucleoli
Areas of Type A are usually present Type A areas not present
Both may be composed of an essentially even mixture of epithelial cells and lymphocytes
Type B2 Thymoma Thymic Lymphoepithelial Carcinoma
Mild cytologic atypia at worst Cytologically atypical
Epithelial cell mitotic figures rare Epithelial cell mitotic figures may be frequent
Lymphocytes are immature T cells Lymphocytes are mature T and B cells



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